1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a facsimile, and a copier.
2. Description of the Related Art
In general, in an image forming apparatus in which an electrostatic photographic process is used, a sheet of paper which is a recording medium placed in a paper tray of a paper feed unit is conveyed to an image forming unit through a paper feed conveyance path by a paper feed apparatus and a toner image formed by an image forming unit is transferred to the paper. The paper to which the toner image is transferred is conveyed to a fixing unit and the toner image on the paper is fixed. The paper on which the toner image is fixed is conveyed to a paper discharge tray through a paper discharge conveyance path or conveyed to a reverse conveyance path. The paper conveyed to the reverse conveyance path is reversed and conveyed to the image forming unit again and a toner image is transferred to the back surface of the paper.
In such an image forming apparatus, when a paper jam occurs, the paper may be left straddling between the paper tray and the paper feed unit. In the case as described above, if an operator carelessly pulls out the paper tray, a so-called forced paper tearing occurs in which the paper is torn and broken into a part on the side of the paper tray and a part on the side of the paper feed apparatus, so that a problem occurs in which a paper removal operation is difficult to be performed.
An image forming apparatus described in Japanese Laid-Open Patent Application No. 2005-084181 is provided with a paper jam detection sensor for detecting a paper jam and an automatic lock mechanism for locking the paper tray to an apparatus main body and unlocking the lock. The automatic lock mechanism includes a lock claw, a solenoid that moves the lock claw to a lock position during ON state in which power is supplied from a power supply, and a release spring that pulls the lock claw to an unlock position during OFF state in which power is not supplied and the solenoid is in OFF state. The paper tray is provided with a fitting hole into which the lock claw of the automatic lock mechanism fits at the lock position. When the lock claw fits into the fitting hole, the paper tray is locked to the apparatus main body.
In the automatic lock mechanism, normally, power is not supplied to the solenoid from the power supply, so that the solenoid is in the OFF state. Therefore, the lock claw is pulled by the release spring and located at the unlock position, so that the lock claw does not fit into the fitting hole provided in the paper tray. Hence, the paper tray can be pulled out from the apparatus main body. When an occurrence of a paper jam is detected by a paper jam detection means, power is supplied to the solenoid from the power supply to cause the solenoid to be in the ON state, the lock claw is moved to the lock position, and the lock claw is fitted into the fitting hole of the paper tray. Thereby, the paper tray is locked to the apparatus main body at a predetermined position and the paper tray is prevented from being pulled out. The image forming apparatus has a configuration as described above, so that it is possible to prevent the forced paper tearing as described above from occurring.
When an image forming apparatus is provided with a drawer unit such as a paper tray, if the drawer unit protrudes from the apparatus main body by vibration during transportation, vibration caused by an earthquake, and the like, there is a risk that the drawer unit and a user collide with each other and the user is injured. Therefore, it is considered that the drawer unit is put into a state in which the unit is locked to the apparatus main body by the automatic lock mechanism even when no paper jam occurs so that the drawer unit does not protrude from the apparatus main body by vibration or the like.
However, when the image forming apparatus is transported or when the image forming apparatus is not used for a long time, normally, the power supply of the apparatus is turned off. Therefore, if the power supply of the apparatus is in an OFF state due to transportation or the like, the solenoid is in the OFF state in the automatic lock mechanism and the lock claw is pulled by the release spring to be located at the unlock position, so that the drawer unit is not locked by the automatic lock mechanism. Hence, when the power supply of the apparatus is in an OFF state due to transportation or the like, it is not possible to prevent the drawer unit from being protruded from the apparatus main body by vibration or the like.
On the other hand, as the automatic lock mechanism, it is considered that a lock claw that can move between the lock position and the unlock position by being driven by a drive means to which power is supplied from the power supply is provided. The drawer unit is locked by the automatic lock mechanism in a state in which the power supply of the apparatus is turned on in advance, so that even if the power supply of the apparatus is turned off thereafter, the lock by the automatic lock mechanism is maintained and it is possible to prevent the drawer unit from protruding from the apparatus main body by vibration or the like.
However, in the automatic lock mechanism having a configuration as described above, when the power supply of the apparatus is OFF, the lock claw cannot be driven by the drive means and the lock by the automatic lock mechanism cannot be unlocked, so that the drawer unit cannot be pulled out. Therefore, when the drawer unit is pulled out and maintenance is performed in a state in which the power supply is OFF, it requires a certain amount of time since it is necessary to perform an operation to unlock the automatic lock mechanism after turning on the power supply of the apparatus. Thus, there is a problem that workability is degraded.
Therefore, there is a need to provide an image forming apparatus that can pull out the drawer unit even when the power supply is OFF while preventing the drawer unit from protruding by vibration or the like.